This material doesn't need to be stolen. It is almost as readily available as sawdust (which can also be made into an explosive). Dirt cheap as well.
I'm still thinking it was the truck that was stolen and the nitrate was just in there. They probably dumped it to get rid of the stuff cause they had no use for it and didn't want to have it taking up space in somebodys garage. The covering of sticks was probably just to put a bit of time between them and the dumpsite, not to keep it's location a big secret.
Tsk Tsk. Always sensationalizing things, aren't we? Ammonium nitrate has a variety of non-explosive related uses.
Whose to say it wasn't stolen by some black market beet farmers, for example?
Whoever it was, you know it was Democrats. It's always Democrats when fertilizer is involved. . .